Tire repair and tire retreading is well known in the art. It is also well known that some level of inspection of the tires prior to repair or retreading is normally conducted to determine whether it is appropriate to perform the operation. While in some instances inspection may include simple visual inspection, it is often important in the case of retreading to determine the condition of internal components of the tire including, for example, voids in the tire's sidewall that may have developed as a result of delamination of the tire materials.
Such inspections have been performed using x-ray analysis based upon visual or shearographic image inspection. Frequently shearographic image inspection is actually followed by x-ray inspection to determine if an identified abnormality is related to the casing wires. Shearographic images can be qualitative in their result and x-ray usage can be subject to regulatory restrictions. Such method can also be time consuming and the required equipment is expensive to own and operate. It would be advantageous, therefore, to develop apparatus and methodologies that eliminate the need for some of these expensive and time-consuming methods. It would also be advantageous to have an apparatus and methodology that produce more detail results and with a more quantitative assessment of the internal state of the tire.
Microwave imaging methodologies are one alternative that may solve the problem stated above. Microwave and millimeter-wave signals span the frequency range of ˜300 MHz to 30 GHz and 30 GHz to 300 GHz, corresponding to the wavelengths of 1,000 mm to 10 mm and 10 mm to 1 mm, respectively, Signals at these frequencies can easily penetrate inside dielectric materials and composites and interact with their inner structures. For material characterization purposes, this interaction may take the form of reflections from undesired flaw boundaries, such as disbands, delaminations, and voids. The relatively small wavelengths and wide bandwidths associated with these signals enable the production of high spatial-resolution images of materials and structures. The availability of a wide array of probes and transducers coupled with signal polarization diversity and coherence (magnitude and phase information) properties can be effectively manipulated for enhancing measurement accuracy and robustness. Optimization of measurement techniques and parameters can also significantly improve interior flaw detection capability.